Organometallic Compounds

Synthesis of Organometallic Compounds

In many compound families, such as alcohols, ethers, amines, and alkyl halides, a carbon atom is connected to a more electronegative atom, such as oxygen, nitrogen, or a halogen. The corresponding carbon in these compounds is positively polarized and, thus, more or less electrophilic. As a result, it may be attacked by a nucleophile.

Fig.1

Carbon nucleophiles may be generated, for instance, through deprotonation of carbonyl compounds in α position. However, in these cases, the product still contains a carbonyl oxygen. If a pure alkyl nucleophile is to be desired, the carbon must be bound to a considerably less electronegative atom in comparison. The carbon is then negatively polarized and, thus, nucleophilic.

Fig.2

Metal atoms usually have a lower electronegativity than carbon does. Therefore, many organometallic compounds were constructed in order to supply carbon (alkyl) nucleophiles. The widely used organolithium compounds, for instance, may be synthesized through treatment of an alkyl halide with lithium in a non-polar solvent, such as hexane.

Fig.3

Synthesis of organolithium compounds.

Another family of organometallic compounds that are often applied are organomagnesium halides, which are also called Grignard compounds (after Francois Auguste Victor Grignard). They are produced through the corresponding reaction between an alkyl halide and magnesium in diethyl ether or tetrahydrofuran (THF). In contrast to lithium, magnesium is formally inserted into the carbon-halogen bond, as magnesium is a dyadic element.

Fig.4

Synthesis of organomagnesium halides.

A number of organometallic compounds such as organolithium compounds and organomagnesium halides are considerably reactive. As a result, they must be carefully treated. A solution of tert-butyllithium in hexane, for instance, spontaneously ignites when it comes into contact with air, as the reaction between tert-butyllithium and air humidity is extremely vigorous.